feat(analytics): integrate analytics across remaining UI components

- Add slash command tracking:
  - Track command selection with method (click/keyboard/autocomplete)
  - Monitor command execution with parameters and timing
  - Record custom command creation events
- Enhance agent execution tracking:
  - Track agent lifecycle (start, progress, completion)
  - Monitor agent errors with retry context
  - Record execution duration and success metrics
- Add tab management analytics:
  - Track tab creation and closure events
  - Monitor active tab switches
- Implement timeline navigation tracking:
  - Track checkpoint navigation events
  - Monitor timeline interactions
- Update useAnalytics hook with comprehensive event helpers
- Export performance monitoring hooks from central index

This completes analytics integration across all major UI components
for full user interaction visibility.